Relative Acoustic Transmission of Topical Preparations Used With Therapeutic Ultrasound

Abstract Objective To determine the relative acoustic transmission allowed by various preparations at 1MHz and 3MHz ultrasound (US) frequencies. Design Bench-top laboratory study. Setting Laboratory. Participants No human or animal participants were used. Interventions We administered continuous US through various over-the-counter preparations at 1.2W/cm2 at both 1MHz and 3MHz frequencies for 30 seconds and measured the acoustic output. Main Outcome Measures Percentage of transmission of energy relative to commercial US gel. Planned observational comparisons were made at both 1MHz and 3MHz frequencies. Topical agents were categorized as either gel-based or cream-based preparations. Results Transmission of gel-based preparations (1MHz and 3MHz): Arnica gel (97% and 110%), Biofreeze (60% and 79%), Capzasin (70% and 93%), Cobroxin (76% and 91%), and Solarcaine (70% and 101%). Cream-based preparations (1MHz and 3MHz): Arnica cream (67% and 74%), Australian Dream (54% and 80%), Bengay (37% and 55%), MediPeds Footcare (126% and 101%), Neuragen PN (76% and 90%), Octogen (38% and 47%), and Thera-Gesic (52% and 73%). Conclusions Topical agents suspended in aqueous gels are generally more effective in transmitting US energy, while many cream-based agents are less effective, particularly at 1MHz frequency. Many agents that are commonly used to provide a sensory effect, such as topical analgesic creams, may block US transmission. Agents that reduce US transmission may lead to poor phonophoresis results and are likely to minimize the therapeutic effects of US.